Photoacoustic and photopyroelectric investigations of thermal parameters in water mixed with organic liquids

Two photothermal (PT) techniques have been applied for investigation of some water-based binary liquid mixtures. Photopyroelectric (PPE) method in back configuration, using the sample thickness scan of the phase of the PPE signal, has been applied for thermal diffusivity measurements. Thermal effusivity investigation has been performed using photoacoustic (PA) open cell with microphone recording. A linear dependence of thermal effusivity on mass concentration of a liquid admixture was observed in the case of non-interacting liquids. For the case of interacting liquids the dependence of relative excess values of both thermal diffusivity and effusivity on mass fraction revealed distinct minima. The results of the PT experiments have been analysed with a simple theoretical model. Adiabatic compressibility variation versus mole fraction of the liquid admixture was also determined, by means of ultrasonic method, for comparison purposes. The obtained PT results support the conclusions drawn from the investigation of the elastic parameter

An active thermography approach for thermal and electrical characterization of thermoelectric materials

International audienceThe enhancement of figure of merit (ZT) of thermoelectrics is becoming extremely important for an efficient conversion of thermal energy into electrical energy. In this respect, reliable measurements of thermal and electrical parameters are of paramount importance in order to characterize thermoelectric materials in terms of their efficiency. In this work, a combined theoretical-experimental active thermography approach is presented. The method consists of selecting the right sequential interdependence between the excitation frequency and the sampling rate of the infrared camera, by computing a temporal Fourier analysis of each pixel of the recorded IR image. The method is validated by using a reference sample which is then applied to a recent synthesized titanium trisulphide thermoelectric material (TiS 3 ). By combining AC and steady-state experiments, one can obtain information on both thermal and electrical parameters of TE materials (namely thermal diffusivity, Seebeck coefficient). The thermal diffusivity and thermal conductivity of TiS 3 are also measured using photothermal radiometry technique (PTR) and the resulting values of these parameters are α = 9.7 ∗ 10 -7 m 2 s -1 and k = 2.2 W m -1 K, respectively. The results obtained with the two techniques are in good agreement. In the case of TE materials, the main benefit of the proposed method is related to its non-contact nature and the possibility of obtaining the electric potential and temperature at the same probes. The Seebeck coefficient obtained by active IR thermography (S = -554 μV K -1 ) is consistent with the one obtained using an ULVAC-ZEM3 system (S = -570 μV K -1 ). For a large number of users of thermographic cameras, which are not equipped with a lock-in thermography module, the present approach provides an affordable and cheaper solution. © 2016 IOP Publishing Ltd

An active thermography approach for thermal and electrical characterization of thermoelectric materials

The enhancement of figure of merit (ZT) of thermoelectrics is becoming extremely important for an efficient conversion of thermal energy into electrical energy. In this respect, reliable measurements of thermal and electrical parameters are of paramount importance in order to characterize thermoelectric materials in terms of their efficiency. In this work, a combined theoretical-experimental active thermography approach is presented. The method consists of selecting the right sequential interdependence between the excitation frequency and the sampling rate of the infrared camera, by computing a temporal Fourier analysis of each pixel of the recorded IR image. The method is validated by using a reference sample which is then applied to a recent synthesized titanium trisulphide thermoelectric material (TiS 3 ). By combining AC and steady-state experiments, one can obtain information on both thermal and electrical parameters of TE materials (namely thermal diffusivity, Seebeck coefficient). The thermal diffusivity and thermal conductivity of TiS 3 are also measured using photothermal radiometry technique (PTR) and the resulting values of these parameters are α = 9.7 ∗ 10 -7 m 2 s -1 and k = 2.2 W m -1 K, respectively. The results obtained with the two techniques are in good agreement. In the case of TE materials, the main benefit of the proposed method is related to its non-contact nature and the possibility of obtaining the electric potential and temperature at the same probes. The Seebeck coefficient obtained by active IR thermography (S = -554 μV K -1 ) is consistent with the one obtained using an ULVAC-ZEM3 system (S = -570 μV K -1 ). For a large number of users of thermographic cameras, which are not equipped with a lock-in thermography module, the present approach provides an affordable and cheaper solution. © 2016 IOP Publishing Ltd

Non-destructive Measurement of Total Carotenoid Content in Processed Tomato Products : Infrared Lock-In Thermography, Near-Infrared Spectroscopy/Chemometrics, and Condensed Phase Laser-Based Photoacoustics—Pilot Study

Carotenes found in a diversity of fruits and vegetables are among important natural antioxidants. In a study described in this paper, the total carotenoid content (TCC) in seven different products derived from thermally processed tomatoes was determined using laser photoacoustic spectroscopy (LPAS), infrared lock-in thermography (IRLIT), and near-infrared spectroscopy (NIRS) combined with chemometrics. Results were verified versus data obtained by traditional VIS spectrophotometry (SP) that served as a reference technique. Unlike SP, the IRLIT, NIRS, and LPAS require a minimum of sample preparation which enables practically direct quantification of the TCC